Alfalfa also known as lucerne is a popular forage crop grown around the world. It is highly valued for its nutritious hay and ability to fix nitrogen in the soil. However, alfalfa has high water requirements and can be challenging to irrigate efficiently. So how much water does an alfalfa plant really need?
Water Requirements Vary
There is no single answer when it comes to alfalfa’s water needs. Recommended water application rates typically range from 20 to 46 inches per season. However, the actual amount can vary significantly depending on climate, elevation, length of growing season, number of cuttings, latitude, and fall dormancy rating of the variety.
In cooler northern climates with a shorter growing season, alfalfa may only need 20-25 inches Meanwhile, in hot southern regions with a longer season and more cuttings, alfalfa may require over 40 inches. Higher elevations and dormant fall varieties also generally need less water.
Average Range
A commonly cited range for alfalfa water requirements is 25 to 35 inches per season This accounts for most growing regions and management systems, Within this range
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Desert regions and lower elevations typically need 30-35 inches.
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Cooler climates and higher elevations can often get by with 25-30 inches.
So in most cases, irrigating for 30 inches per season is a reasonable starting point. Adjustments can then be made based on local conditions.
Water Use Increases Through Season
It’s important to understand that alfalfa’s water demand is not constant. Water use gradually increases from spring green up through peak summer growing season.
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In early spring, alfalfa may only use 0.5-1 inch/week.
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By early summer, this rises to 1.5 inches/week.
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During peak season, demand can reach 2 inches/week or more.
So frequent irrigation is needed to keep up with demand, especially in mid to late summer. Stress during this period can significantly reduce yields.
Direct Relationship to Yield
There is a direct relationship between water application and alfalfa yield. Studies show yields can increase by 1/5 to 1/6 ton per acre for every inch of water applied, up to about 30 inches total. Beyond this point, additional water provides little extra yield benefit.
On average, alfalfa will use 4-5 inches of water from the soil and irrigation for each ton of hay produced. So the more water available to the crop, the higher the potential yields. However, adequate drainage is also critical to avoid waterlogging.
Fill Soil Profile Before Planting
The best approach is to fill the soil profile with moisture before planting alfalfa. This allows the young seeds and seedlings to germinate and establish with ample available water. Pre-irrigation is highly recommended in dry regions.
Irrigate Frequently During Growing Season
Frequent irrigation during the growing season is needed to replenish soil moisture. Each event should fill the root zone profile, applying 3-4 inches on average. This encourages deep root growth and leaches salts down below the roots.
Stop Irrigating Before Harvest
It is generally recommended to stop irrigating 3-10 days before cutting hay. This allows the soil to dry out a bit, improving traction for harvest equipment and reducing potential for compaction.
Flood Irrigation Requires Caution
Flood irrigation requires extra caution, as prolonged ponding can damage alfalfa stands. It’s best to flood irrigate when water temperatures are cool in early spring or right after cuttings. Quick water movement across fields is also critical.
Monitor Soil Moisture
Careful monitoring of soil moisture levels is important to determine when to irrigate. Checking moisture at 12 and 24 inch depths will provide a clear picture of profile status. Ideal levels are 50-70% of available water capacity.
Alfalfa uses a lot of water Recently harvested alfalfa that became dormant due to drought and high temperatures. It can survive dormancy for months and resume growth when moisture conditions are favorable. Photo: C.C. Sheaffer.
Because of its high stem density and dense canopy, alfalfa has a high rate of water use. Alfalfa uses 0.1 to 0.3 inches of water per day (Table 1).
Daily water use is influenced by plant growth stage and environmental factors like air temperature and wind speed. For example, on a windy, 90° F day in Minnesota, alfalfa will likely use 0.30 inches of water.
Water use is greatest when alfalfa has a full vegetative canopy before harvest and is greater during summer months when solar energy and air temperatures are greatest.
Water use declines following harvests and is less in the spring and fall when the sun’s energy and air temperatures are lower.
| Daily maximum temperature (°F) | 1 week after cutting | 2 weeks after cutting | 3 weeks after cutting |
|---|---|---|---|
| inches/day | inches/day | inches/dat | |
| 50 | 0.05 | 0.06 | 0.08 |
| 60 | 0.08 | 0.11 | 0.13 |
| 70 | 0.11 | 0.15 | 0.19 |
| 80 | 0.15 | 0.19 | 0.23 |
| 90 | 0.19 | 0.23 | 0.28 |
Scherer and Steele, Irrigation Scheduling by the Checkbook Method, 2019.https://www.ag.ndsu.edu/publications/crops/irrigation-scheduling-by-the-checkbook-method-1
Figure 1. Total season yield of alfalfa in relationship to season-long water use from precipitation and/or irrigation.
Crop water use and forage yield
Over the growing season alfalfa may use more total water than other crops because of its long growing season. There is generally a linear relationship between crop water use and forage yield, although aspects of this relationship vary somewhat based on other environmental factors. Water use ranges from 4 to 7 inches per ton of forage depending on the environment (Figure 1).
Alfalfa And Water
FAQ
How often should alfalfa be watered?
Can you overwater alfalfa?
How much moisture does alfalfa need?
How many gallons of water does it take to grow alfalfa?
How much water does alfalfa need?
During the winter, alfalfa will need less water, so you can wait until the soil is dry before watering. When it comes to how much water alfalfa needs, a good rule of thumb is to provide 1-2 inches of water per week. This is best done by setting up a drip irrigation system, which is more efficient and allows for a more even distribution of water.
How much water do you need to irrigate alfalfa hay?
Consequently, the ability of the crop to get off to a good start can have a significant effect on the annual yield. Amount of water to apply: On the average, irrigated alfalfa will use approximately 4 to 5 inches of water for every ton of hay produced.
Can a deep soil capacity sustain alfalfa growth?
A deep soil capacity can sustain alfalfa growth when irrigation is halted for harvest or when the irrigation application rate does not keep up with ET. Yield response to water application is generally linear, but varies with climate. It takes about 6.6 inches of applied water to produce each ton in arid climates.
Can alfalfa be irrigated?
Alfalfa is very sensitive to excess soil water. In addition, air temperature and temperature of the irrigation water appear to significantly affect alfalfa stand longevity. Several studies have compared the growth of roots and forage of alfalfa flood irrigated for various lengths of time and at different temperatures.